Study On The Preparation Technology Of Polycarbonate Diol And Its Performance Simulation

Polycarbonate diol(PCDL)is a new type of polyurethane soft segment material.The polycarbonate polyurethane produced with PCDL as soft segment has the advantages of polyether polyurethane and polyester polyurethane,and has excellent hydrolysis resistance and mechanical properties.Polyurethane elastomer is a kind of polyurethane products with a wide range of uses,but the high price has a certain impact on its market development.Microporous polyurethane elastomer has low density,which can reduce the production cost.It also has the advantages of light weight,easy deformation and molding.According to the processing method,it can be divided into mixing type,pouring type and thermoplastic microporous polyurethane elastomer.The thermoplastic microporous polyurethane elastomer can be made by TPU process and adding foaming agent in the molding process.E-TPU is a product processed by TPU,and its foaming agent is usually supercritical CO₂ fluid.The dissolution and diffusion of supercritical CO₂ in polyurethane soft segment material has an important influence on controlling the microcellular structure of foaming.In this paper,polyhexamethylene carbonate diol(PHCD)was synthesized by transesterification from dimethyl carbonate(DMC)and 1,6-hexanediol with sodium methoxide as catalyst.The effect of catalyst dosage on the conversion of hexanediol was studied;the process conditions such as molar ratio of feedstock,total reaction time at atmospheric pressure,total reaction time at reduced pressure and reaction temperature at reduced pressure were studied;the hydroxyl value,T_c,T_g and T_m of the product were studied.The results show that:the optimum amount of catalyst is 0.7%of the mole ratio of hexanediol;increasing the proportion of DMC is conducive to the chain growth of PHCD,but not conducive to the hydroxyl end capping of the product;prolonging the total reflux reaction time in the atmospheric pressure reaction stage can improve the utilization rate of DMC;prolonging the total pressure reduction reaction time and increasing the decompression reaction temperature are conducive to the chain growth of PHCD and the hydroxyl end capping of the product.The number average molecular weight was positively correlated with T_c,T_g and T_m.Then,molecular dynamics simulation was used to study the dissolution and diffusion behavior of supercritical CO₂ in PHCD.The influence of temperature and pressure on the dissolution and diffusion behavior of supercritical CO₂ in PHCD was studied by calculating the solubility parameters,diffusion coefficient and free volume fraction.The results show that:the influence of temperature and pressure on the compatibility of supercritical CO₂ and PHCD mainly comes from their influence on the solubility parameters of supercritical CO₂;the higher the temperature is,the worse the compatibility is;the higher the pressure is,the better the compatibility is;the decrease of pressure and the increase of temperature are conducive to the diffusion of supercritical CO₂ in PHCD;the diffusion coefficient of supercritical CO₂ in PHCD is less affected by pressure and more affected by temperature;the increase of temperature causes the thermal expansion of PHCD,and then increases its free volume fraction,which promotes the diffusion of supercritical CO₂ in PHCD.